Does evolution always lead to bigger brains?

Homo floresiensis, a pygmy-sized small-brained hominin popularly known as 'the Hobbit' was discovered five years ago, but controversy continues over whether the small brain is actually due to a pathological condition. How can its tiny brain size be explained?

Researchers writing in the open access journal BMC Biology have tackled this question in the context of a comprehensive assessment of the evolution of brain and body size throughout the larger primate family.

Dr Nick Mundy and Stephen Montgomery, from the Department and colleagues from Durham University used previously published data from living and extinct species to reconstruct the pattern of brain and body mass evolution in primates. Nick Mundy explains: "A trend towards brain expansion is assumed to have occurred throughout primate evolution. This has been interpreted as an indication of selection for cognitive abilities due, for example, to 'arms races' in the ability to process social information."

"We found decreases in brain mass along several branches across the primate family tree. It is likely that reductions in brain size occurred to meet demands of the species' changing ecological needs meaning that sometimes individuals with smaller brains are favoured by natural selection."

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